mirror of
https://github.com/Dasharo/systemd.git
synced 2026-03-06 15:02:31 -08:00
b8df7f8629
So far we didn't enable the cpu controller because of overhead of the accounting. If I'm reading things correctly, delegation was enabled for a while for the units with user and pam context set, i.e. for user@.service too.a931ad47a8added the explicit Delegate=yes|no switch, but it was initially set to 'yes'.acc8059129disabled delegation for user@.service with the justication that CPU accounting is expensive, but half a year latera88c5b8ac4changed DefaultCPUAccounting=yes for kernels >=4.15 with the justification that CPU accounting is inexpensive there. In my (very noncomprehensive) testing, I don't see a measurable overhead if the cpu controller is enabled for user slices. I tried some repeated compilations, and there is was no statistical difference, but the noise level was fairly high. Maybe better benchmarking would reveal a difference. The goal of this change is very simple: currently all of the user session, including services like the display server and pipewire are under user@.service. This means that when e.g. a compilation job is started in the session's app.slice, the processes in session.slice compete for CPU and can be starved. In particular, audio starts to stutter, etc. With CPU controller enabled, I can start start 'ninja -C build -j40' in a tab and this doesn't have any noticable effect on audio. I don't think the particular values matter too much: the CPU controller is work-convserving, and presumably the session slice would never need more than e.g. one 1 full CPU, i.e. half or a quarter of available CPU resources on even the smallest of today's machines. app.slice and session.slice are assigned equal weights, background.slice is assigned a smaller fraction. CPUWeight=100 is the default, but I wrote it explicitly to make it easier for users to see how the split is done. So effectively this should result in session.slice getting as much power as it needs. If if turns out that this does have a noticable overhead, we could make it opt-in. But I think that the benefit to usability is important enough to enable it by default. W/o something like this the session is not really usable with background tasks.
System and Service Manager
Details
Most documentation is available on systemd's web site.
Assorted, older, general information about systemd can be found in the systemd Wiki.
Information about build requirements is provided in the README file.
Consult our NEWS file for information about what's new in the most recent systemd versions.
Please see the Code Map for information about this repository's layout and content.
Please see the Hacking guide for information on how to hack on systemd and test your modifications.
Please see our Contribution Guidelines for more information about filing GitHub Issues and posting GitHub Pull Requests.
When preparing patches for systemd, please follow our Coding Style Guidelines.
If you are looking for support, please contact our mailing list or join our IRC channel.
Stable branches with backported patches are available in the stable repo.